This invention relates to a surface mount electrical resistor with thermally conductive, electrically non-conductive filler and method for using same.
Electronic systems such as cell phones, computers, consumer electronics and the like continue to get smaller and smaller. As the systems shrink in size, smaller electronic components are required. However, the power requirements of the system are not necessarily reduced in magnitude as the electronic systems and their components get physically smaller. Therefore, the heat generated by the components must be managed so as to maintain safe and reliable operating temperatures for the systems.
Resistors are a primary component in the electronic circuit assemblies of these various systems. Prior art resistors have many different designs. Some prior art resistors have terminations that are very short, in comparison to the length of the resistive element, and extend outwardly from the ends of the resistive element. Other prior art resistors have terminations that are long and wrapped underneath the resistive element, but are not optimized for thermal conductivity from the resistive elements, thereby precluding any significant improvement in heat dissipation. Still other prior art terminations for heat dissipation are not used for electrical connection to the circuit assembly. Yet other prior art terminations serve primarily as the electrical connection to a printed circuit board, but also provides the primary means for removing heat from the resistive element. However, all of these prior art terminations have limited size or thermal efficiency and therefore limited capacity for heat dissipation.
Examples of prior art resistors are shown in FIGS. 1 and 2. In FIG. 1, a resistor 11 having a protective coating 30A surrounding a resistance element (not shown) also includes terminals 24A and 25A. The terminals are soldered to pads 12. Only air exists beneath the protective coating 30A, and therefore heat dissipation from the resistance element within 30A is less than is desired.
Another form of prior art resistor 110 is shown in FIG. 2. This resistor 110 includes a resistance element 114 having terminals 124 and 125 bent down beneath the resistance element 114. A coating material 128 surrounds the resistance element 114 and is positioned between the resistance element 114 and the leads 124, 125. As can be seen in FIG. 2, the thickness of the material 128 is represented by the numeral T1, and this is approximately 0.381 mm (which is approximately 15 mils). The thickness of the resistance element itself 114 is represented by the numeral T2 and is approximately 0.1270 mm (5 mils). The material 128 surrounding the resistance element 114 is not attached to or bonded to the leads 124 or 125, but instead the leads 124 or 125 are bent around and into contact with the material 128 after the material 128 has cured and hardened. Furthermore, the thickness T1 is so great as to prevent the enhancement of heat conduction from the resistance element 114 through the material 128 to the leads 124 or 125.
Therefore, a primary objective of the present invention is the provision of an improved electrical resistor having enhanced heat dissipation.
Another objective of the present invention is the provision of a surface mount electrical resistor having a resistive element with terminations extending from the opposite ends of the resistive element and extending under, and in close proximity to [between 0.0254 mm and 0.254 mm (1 mil to 10 mils)], the resistive element.
A further objective of the present invention is the provision of an improved electrical resistor having terminations which provide both electrical and enhanced thermal conductivity from the resistive element.
A further objective of the present invention is the provision of a method of making an electrical resistor including the step of extending the terminations under the resistive element so that a thermally conductive and electrically insulated filler material of minimal thickness is sandwiched between the resistive element and the terminations prior to curing the filler material.
A further objective of the present invention is the provision of a resistor wherein the filter material is bonded both to the resistive element and the two terminations so as to enhance heat conduction from the resistive element to the terminations.
Yet another objective of the present invention is the provision of a surface mounted electrical resistor which is economical to manufacture and which functions at a lower temperature than prior art resistors of equal size and power load.
These and other objectives will become apparent from the following description of the invention.